What the test measures
Air tightness testing (also called air permeability or air pressure testing) shows how much air leaks through a building’s envelope. The more airtight the building, the less heat escapes — and your SAP calculation will have assumed a specific air tightness figure to achieve its pass, so the test result must back it up.
A large fan is temporarily fitted into an external doorway and run at a series of speeds, blowing air in or drawing it out. The result — q50, in m³/hour/m² of envelope area — measures leakage at 50 Pascals. (Passivhaus projects use n50, air changes per hour.) Part L 2021 caps q50 at 8.0 in SAP, but the notional dwelling assumes 5.0, and 5.0 or better is what most projects need and achieve.
How to pass first time: the pre-test checklist
Most failures are simple sealing issues. Before we arrive, check:
- Gaps in and around suspended timber floors, and floor-to-wall joints (especially timber frame)
- Leaky or poorly sealed windows and doors, and gaps around frames
- Ceiling-to-wall joint at the eaves; gaps around loft hatches
- Service penetrations through ceilings; vents penetrating ceiling or roof
- Kitchen and bathroom wall vents and extractor fans; gaps around waste pipes
- Open chimneys; gaps around electrical fittings in hollow walls
- All boxing sealed; backs of toilets (especially wall-hung WCs)
Allowed temporary sealing: fireplaces and woodburners, extractor fans and passive vents, and trickle vents (2013 regs onwards).
Print it, walk the site and tick each item off before we arrive. Includes the temporary-sealing do's and don'ts and the SAP note on untested plots. No sign-up.
Booking
We test dwellings and commercial buildings across the south and beyond, and can bundle testing with your SAP work — see the Compliance Pack. Get a quote or call 01202 623236.